When are thin films of metals metallic? Part III

A large amount of experimental information has indicated that very thin films of metallic elements can exhibit nonmetallic behavior, even on metal substrates. These films undergo a gradual nonmetal to metal transition with increasing film density or thickness. The nonmetallic behavior can be related to electron localization due to strong electron-electron correlation in low dimensional systems, as indicated by the strong enhancement of electron effective mass. The evolution in the electronic structure associated with the nonmetal to metal transition bears a striking resemblance to the behavior observed for free metal clusters. Part I [1], outlined the general concepts of a nonmetal to metal transition in a thin film, while part II [2] critically examined three examples of nonmetal to metal transitions for thin film overlayers. This paper will discuss some surprising correlations between the electronic structure of divalent thin films on metal substrates and divalent metal clusters that have been reported in the literature.